Leaf development occurs through the coordinated temporal and spatial regulation of various genes and genetic programs. Studies of maize mutants that affect spatial development have led to the identification of several genes required for properly drawing morphogenetic fields or domains. Genes controlling the temporal aspect of leaf development have not been cloned. The goal of this proposal is to further our understanding of maize leaf development by cloning and characterizing the timekeeping gene lax midrib1 that affects leaf development. Two strategies will be used to accomplished this goal. Both approaches utilize the maize mutant Lax midrib1-Original (Lxm1-O) and focus primarily on leaf development. The first approach explores how genes regulate or control "timing" during development of the leaf and involves cloning lxm1 and determining where and when lxm1 is expressed. The second approach will determine which phase or phases of leaf organogenesis lxm1 affects.